Control devices for gas turbine power plants

ABSTRACT

A control device for a gas turbine power plant of the type comprising a compressor, a combustion chamber supplied with air coming from the compressor and with fuel, a turbine supplied with combustion gases coming from the combustion chamber, and a nozzle which discharges the combustion gases coming from the turbine, said control device comprising means for metering the fuel flow to the combustion chamber and means for varying the crosssectional area of the nozzle, wherein the means for varying the cross-sectional area of the nozzle is controlled as a function of the fuel flow rate C delivered to the combustion chamber, the static air pressure P2 at exit from the compressor, and the static gas pressure Ps at the turbine exit, so that at least under certain conditions of operation, an output quantity defined by the expression c/( Beta Ps - Ps ), in which Beta designates a constant coefficient of reduction, has a desired predetermined value.

United States Patent Briotet et al.

[ 1 March 6, 1973 Societe Nationale DEtude et de Construction deMonteurs dAviation, Paris, France Filed: Feb. 3, 1971 Appl. No.: 112,272

[73] Assignee:

[30] Foreign Application Priority Data Feb. 4, 1970 France ..7003923U.S.'Cl. ..60/239, 60/39.09 R

Int. Cl "F02k 11/00 Field of Search.. 60/235, 236, 238, 239, 39.09 R

References Cited UNITED STATES PATENTS Rogers ..60/238 1/1967 Aubert..60/237 4/1967 Tissier ..60/238 Primary Examiner-Douglas HartAttorney-William J. Daniel [57} ABSTRACT A control device for a gasturbine power plant of the type comprising a compressor, a combustionchamber supplied with air coming from the compressor and with fuel, aturbine supplied with combustion gases coming from the combustionchamber, and a nozzle which discharges the combustion gases coming fromthe turbine, said control device comprising means for metering the fuelflow to the combustion chamber and means for varying the cross-sectionalarea of the nozzle, wherein the means for varying the cross-sectionalarea of the nozzle is controlled as a function of the fuel flow rate Cdelivered to the combustion chamber, the static air pressure P at exitfrom the compressor, and the static gas pressure P, at the turbine exit,so that at least under certain conditions of operation, an outputquantity defined by the expression C/(BP P,,), in which B designates aconstant coefficient of reduction, has a desired predetermined value.

12 Claims, 3 Drawing Figures PATENTEU 975 SHEET 2 or 2 CONTROL DEVICESFOR GAS TURBINE POWER PLANTS The present invention relates to a controldevice for a gas turbine power plant, in particular for aircraft jetpropulsion applications, of the type comprising a compressor, acombustion chamber supplied with air coming from the compressor and withfuel, a turbine supplied with combustion gases coming from thecombustion chamber, and a nozzle which discharges the combustion gasescoming from the turbine, said device comprising means for metering,i.e., regulating, the fuel flow to the combustion chamber and means forvarying the cross sectional area of the nozzle.

The object of the invention is to improve existing control devices bothfrom the point of view of their 'flexibility and reliability and fromthat of their performance.

As those skilled in the art will be aware, for a given compressor speed,there is a relationship between the cross-sectional area of the nozzleand the gas temperature at the turbine intake, which makes it possibleto control said temperature by varying said cross sectional area. Thiskind of control, in particular, makes it possible to compensate for thesubstantial variations to which said temperatures is subject whenexternal conditions such as the speed and altitude of an aircraftpropelled by the gas turbine power plant, vary, and also makes itpossible to maintain this temperature at a selected value so that thehighest possible efficiency is achieved at all times whilst beingcompatible with the temperature which the turbine blading willwithstand.

However, difficulties arise in accurately determining by directmeasurement, the temperature of the gases at the turbine intake, thesedifficulties arising in particular from the non-uniformity of thethermal field and the thermal inertia of the temperature detectingdevice. Also, various devices have been proposed in which said directmeasurement is replaced by an indirect measurement in the form of theproduction of a signal which takes account of the instantaneous valuesof various factors which could influence said temperature, in accordancewith a theoretical or experimental law.

The present invention falls within the scope thus defined, i.e., comesunder the heading of the case in which the temperature of the gases,measured indirectly, is regulated by varying the nozzle cross-sectionalarea and it relates, in a first aspect, to the definition of a controllaw which, in a simple but nevertheless more accurate fashion than theknown laws, expresses the reality of the physical phenomena which are atwork.

To this end, in accordance with this aspect of the invention and in acontrol device of the kind above.

described, the means for varying the cross-sectional area of thenozzle'is controlled as a function of the fuel flow rate C delivered tothe combustion chamber, the static air pressure P", at exit from thecompressor, and the static gas pressure PB, at the turbine exit, so thatat least under certain conditions of operation, an output quantitydefined by the expression C in v u a-, which B designates a constantcoefficient of reduction, has a desired predetermined value. As will beseen hereinafter, said predetermined value can be adjusted for exampleas a function of the position of a pilotoperated control lever in theaircraft, in order to take account of the load and possibly of otherparameters associated with the power plant.

The law of control thus chosen has various practical advantages, inparticular when applied to a dual-flow power plant with an after-bumerfitted. Amongst these advantages we can point in articular to aconsiderable improvement in the accuracy of the indirect control of thegas temperature upstream of the turbine (and therefore to acorresponding increase in the power plant efficiency by reason ofreduction in the safety margin which has been necessary hitherto), anincrease in the sensitivity to load variations during operation in theafter-buming configuration (and consequently reduction in theacceleration and deceleration times in said configuration), and, in thecase of a dual-flow .power plant, a reduced sensitivity to the tappingoff of air and power from the secondary duct of the power plant.

As explained in detail hereinafter, the control device in accordance'with the invention comprises means by which to produce, as a functionof the fuel flow-rate C delivered to the combustion chamber and thestatic pressures first of all P5, of the air at the exit from thecompressor and secondly PB of the gases at the exit from the turbine, afirst signal which is a function of the output quantity 0 means forproducing a second signal or reference signal B s P57 which is afunction of said desired predetermined value means for producing a thirdsignal or error signal which is a function of the difference C 6 minusand means sensitiveto said B a P57 error signal in order to control thevariation in the cross-sectional area of the nozzle.

The implementation of these various means obviously requires properoperation of an automatic signalprocessing device, for example anelectronic device. Serious consequences as far as the thermal integrityof the turbine blading is concerned, could therefore result from abreak-down or failure in said processing device.

Thus, in accordance with a second aspect, the invention provides for thelimitation of the damage which could arise from such a failure, bysimple and efficient emergency manual control (which could also beimplemented in order to back up automatic temperature control of adifferent kind to that described hereinbe fore), which has the featureof using, as control factor, the fuel flow rate supplied to thecombustion chamber.

In accordance with one arrangement which is concerned with this aspectof the invention, the means used to regulate the fuel flow to thecombustion chamber are controlled as a function of the fuel flowrate Cdelivered to said combustion chamber and of the static pressure P of theair at the compressor exit, so that an output quantity defined by theratio C is maintained at a predetermined desired value which can bemodified through the agency of the manual emergency control referred tohereinbefore. It is thus possible, within certain limits fixed by therange of operation of the pilot-operated control lever, to vary thevalue of the ratio C To each value of this ratio, there then with anapproximately constant gas temperature at the turbine intake.

In accordance with an advantageous arrangement, a

.disengageable coupling can be arranged between the emergency manualcontrol and the means used to regulate the fuel flow rate, in order, innormal operation, to eliminate any interference between the manualcontrol and the automatic control. This coupling can, for example, bebiased into its engaged position under the action of the pressure of acontrol fluid, said action being consequent upon the opening of a valvedevice arranged between a source of said, control fluid and thecoupling.

In accordance with another feature of the invention, means can beprovided in order to urge into their fully open position, the means usedto vary the cross-sectional area of the nozzle, this when said couplingis in the engaged position, that is to say when the emergency controlsystem is in operation. In this fashion, possible inopportune variationsin the cross-sectional area of the nozzle, which, despite theintervention of the emergency control, could give rise to a dangerousincrease in the gas temperature at the turbine intake, are avoided.

Inaccordance with a preferred embodiment of the invention, these urgingmeans can comprise means sensitive to the pressure of the couplingcontrol fluid, said pressure being tapped off between said coupling andthe valve device.

The description which now follows in relation to the attached drawings,given here by way of a non-limitative example, will indicate how theinvention may be put into effect.

FIG. 1 is a much simplified view of a gas turbine power plant equippedwith a control device in ac cordance with the invention FIG. 2 is aschematic view of said control device FIG. 3 is a view on a largerscale, of a detail of FIG. 2.

In FIG. 1, the general reference 1 has been used to indicate a gasturbine power plant constituted in the present case by a basic turbojetengine designed for the propulsion ofa flying machine such as anaircraft. Said turbojet engine comprisesfollowing an air-intake 2, acompressor with a low-pressure section 3 and a highpressure section 4, acombustion chamber 5, a turbine constituted by a high-pressure stage 6and a low-pressure stage 7, an after-burner section 8 with burners 9,and a nozzle 10 for discharging the combustion gases,

these latter possibly being re-heated in the after-burner section 8 onexit from the turbine.

Means such as flaps 1], enable the cross-sectional area of the nozzle10, which we shall mark by the letter possible to control the effectiveflow rate which we will her designate by C, of the fuel delivered to thecombustion chamber 5. These means can advantageously comprise avariable-area orifice associated with means for maintaining the fuelpressure drop across said orifice, constant.

The turbojet engine 1 can be of the single-flow or dual-flow kind, thisbeing symbolized by the presence of a branch duct 19, illustrated inchain-dotted fashion, coupled to the output of the low-pressure stage 3of the compressor and enabling a certain proportion of the air deliveredby said stage to be tapped off.

A pilot-operated control lever 21 enables the pilot to vary the powerplant load continuously. This control lever is associated with a controldevice marked by the general reference R which constitutes the object ofthe present invention. Said'control device is designed, for eachposition to which the pilot sets his control lever to ensure optimumoperation of the power plant and eliminate mechanical and thermalconditions which could adversely affect its stability and operationallife, this whatever the disturbances (such as variations in atmosphericconditions or changes in altitude or speed of flight of the aircraft) towhich it is subjected.

To this end, it reacts to various signals and as a consequence modifiestwo control quantities constituted respectively by the fuel flow rate Cdelivered into the combustion chamber 5 and the cross-sectional area Sof the nozzle 10. These signals include, in particular signalsrepresenting the staticair pressure at the compress'or exit (which wewill subsequently call P., the static gas pressure at the turbine exit(which we shall subsequently call P the speed of rotation of thecompressor (which we shall subsequently call N), the total temperatureof the air at the compressor intake (which we shall subsequently callT,,), and scheduled signals which are a function, in particular, of theposition of the pilot-operated lever 21.

Considering FIGS. 2 and 3, the control device R in accordance with theinvention will now be described.

The fuel circuit comprises, as we have seen, means 18 for metering theeffective fuel flow rate C to the combustion chamber, said means beingarranged between the pump 14 and the injectors l7. Said means comprise ametering orifice 30 constituted by an opening whose exposedcross-sectional area varies, preferentially linearly as a function ofthe position of a. spool 31 fixed to a servo piston 32. Means such as acontrol valve, which has not been shown, enable the pressure drop of thefuel through the metering orifice 30 to be maintained constant so thatthe fuel flow rate C is itself a linear function of the position of theservo piston 32.

The control of the fuel flow rate is effected by means of a forcebalance in the form of a lever L articulated at a fixed point 0. At oneof the ends L, of said lever, there acts at a moment arm a from thefulcrum O, a force which is generated in a system comprising a capsule33 which is evacuated and a capsule 34 subjected to the static pressureP., of the air delivered by the compressor, said force being thusproportional to the absolute pressure 1 The other end L, of the leveroscillates very slightly between twobleed openings 35, 36 and, as aconsequence of its movement, modulates in one direction or the other thepressures prevailing in two chambers 37, 38 delimited respectively bythe opposite faces of the servo piston 32 and supplied in each case withfuel under pressure.

To servo piston 32 is attached by a spring 39 to a lever 40 articulatedat a fixed point 41. A roller 42 can move between the lever L and thelever 40 without losing contact with said two levers, whatever theposition of the end L of the lever L between the bleed openings 35, 36.The amplitude of oscillation of the lever L being very small, it isreasonable to assume that its displacement is perpendicular to thetravel of the servo piston 3 The roller 42 is secured to a link 43articulated at one of its ends to a lever 44 pivoting about a fixedpoint 45. The other end of the lever 44 bears under the action of aspring 44a against a cam 47 fixed to a rotating shaft 48.

Thus, a relationship can be established between the angular position ofthe shaft 48 and the position of the roller 42, which position can bedefined by the distance b separating said roller from the fulcrum O.

The spring 39 exerts upon the lever L, through the medium of the lever40 and the roller 42, a force F proportional to the tension in saidspring. If we call s the cross-sectional area of the capsules 33, 34,then the lever, in the balanced condition, adopts an angular positionsuch that the following balanced equation obtains P, s0 F b from whichwe obtain The quantities a and s being constant, the result is that theratio F is a function purely of the distance b,

P., that is to say of the position of the roller 42. For a givenposition of said roller, the ratio F is therefore constant. The lever Land the roller 42 thus define a balanced system of forces with avariable multiplication ratio which is a function of the angularposition of the shaft 48.

If the spring 39 is selected so that its tension varies linearly withits extension, that is to say with the displacement of the servo piston32, then the quantities F and C will be proportional and we cantherefore write 2 l=constant for a given angular position of the shaft48.

This angular position can be detected by a pick-up 49 which produces forexample an electrical signal which is a function of said angularposition and, consequently, of the value of the ratio C correspond- Ping thereto. Two controls, one'automatic and the other manual, enablethe angular position of the shaft 48 to be modified.

The automatic control essentially comprises a motor 50, for example anelectric one, coupled to the shaft 48 through the medium of gears 51, 52and a torquelimiter 53.

The manual control comprises a lever 54 coupled on the one hand with theshaft 48 through the medium of a disengageable coupling 55, and bevelgears 56, 57, and on the other hand to the pilot-operated lever 21through the medium of a linkage 58, 59.

The disengageable coupling 55 comprises, in particular, a drive shaft 60driven by the lever 54, and a driven shaft 61 fixed to the gear 56. Thedrive shaft 60 is fixed to a component 62 in which there are slidablymounted fingers 63 each exhibiting a shoulder 64. The driven shaft 61 isfixed to a plate 65 in which slots 66 of shape corresponding to that ofthe fingers 63, are provided. The said fingers can occupy two positions,namely an operative position or engaged position, in which theypenetrate into the slots 66 in order to couple the drive shaft 60 andthe driven shaft 61, and an inoperative or disengaged position, in whichthey are retracted by return springs 67, into the interior of thecomponent Each of the shoulders 64 can be subjected to the pressure of acontrol fluid which is admitted to a chamber 68 within the coupling. Inthe example illustrated, said control fluid is constituted bypressurized fuel tapped off upstream of the metering means 18, throughthe medium of a pipe 69 in which a valve device is arranged, in thepresent instance a solenoid valve 70. The latter is normally maintainedin the closed position by the action of the fuel pressure prevailing inthe pipe 69, but is open when its electrical circuit, indicated byreference 70a, is switched in.

In normal operation, it is exclusively the automatic control 50, 51, 52,53 which is operative and the coupling 55 is disengaged. The manualcontrol 54, 55, 56, 57 is an emergency control whose function will beexplained hereinafter.

The automatic control 50, 51, 52, 53 forms part of a first controlsystem in which the control quantity or parameter is constituted by theratio (the value P 4 of which is represented by the position of theroller 42 that is to say the angular position of the shaft 48), and inwhich the output quantity or controlled parameter is the speed ofrotation N' of the compressor.

A computer device E, for example an electrical or electronic device, issupplied to this end with a first signal which is a function of theactual speed of rotation N of the compressor as detected by a suitabletachometer, and a second signal N representing a desired speed as set bythe angular position of the pilotoperated lever 21 and possiblycorrected by other parameters such as the total temperature T,, of thecompressor intake air in order, for example, to take account of thealtitude of flight. The device E produces, on the basis of thesesignals, an error signal N N N which, through the medium of the electricmotor 50, controls the angular position of the shaft 48 in aproportional manner [A KAN, A being a constant] or a time-integratingmanner [1 2 J'ANM is adapted to the desired speed of rotation and theexposed cross-sectional area of the metering orifice 30 is such as topass the fuel flow rate C which corresponds to this speed.

In the known fashion, acceleration and deceleration stops (not shown)can be provided in the computer device E in order to limit the value ofC as a func- Pi, tion of parameters such as N or P (total pressure ofthe compressor intake air).

When the emergency control 54, 55, 56, 57 is operated, its actionoverrides that of the automatic control 50, 51, 52, 53 by reason of thepresence of the torque limiter 53 whose setting is appropriatelycalculated.

To the first control system described, a second is added in which thecontrol quantity or parameter is constituted by the cross-sectional areaS of the nozzle and in which the controlled parameter is constituted, inaccordance with one feature of the invention, by a special outputquantity defined by the expression C in which C designates the fuel flowfi q I1 rate injected into the combustion chamber 5, the static airpressure at the compressor exit P. the static gas pressure at theturbine exit, and )3 a predetermined numerical coefficient less thanone.

The applicants have come to consider that this quantity constitutes anindirect but extremely accurate indication of the temperature T of thecombustion gases at the turbine intake, which temperature it is theobject of the control system hereinafter described to maintain, underall conditions of operation of the power plant, at an optimum valuewhich does not introduce any risk of impairment of the thermal stabilityof the turbine blad- A force balances system constituted by a lever Uwith a variable multiplication ratio, articulated about a fixed fulcrumpoint 0,, enables a signal which is a function of the quantity C to begenerated. At

one of its ends U this lever is acted upon, at a moment arm :1 from thefulcrum 0 by a force generated in a system comprising two opposedcapsules of the same cross-sectional area, namely a first capsule 80subjected to the pressure P, and a capsule 81 subjected to a lowerpressure BF This latter pressure is produced, from the pressure P in areducer device comprising a chamber 82 communicating on the one handwith the downstream side of the compressor through the medium of arestrictor K, preferably a variable one, and on the other hand, with theatmosphere (where a pressure P, prevails), through the medium of arestrictor L, for example a fixed one.

The other end U, of said lever cooperates with a rod 83 forming part ofa servo control 84 designed to regulate the cross-sectional area S ofthe nozzle 10, the detail of said servo control having been shown inFIG. 3.

The servo piston 32 forming part of the fuel-metering means 18, actsthrough the medium of a spring 85 on a lever 86 articulated at a fixedpoint 87. A roller 88 can displace between the lever U and the lever 86without losing contact with either of them, this whatever the positionof the end U, of the lever U which cooperates with the rod 83.

The roller 88 is fixed to a link 89 articulated to one of the ends of alever 90 pivoting about a fixed fulcrum point 900. The other end of thelever 90 bears under the action of a spring 91 against the cam 92 fixedto a rotatable shaft 93. Thus, as in the case of lever L describedearlier, a relationship can be established between the angular positionof the shaft 93 and the position of the roller 88, which position can bedefined by the distance b separating said roller from the fulcrum point0,.

The spring 85 exerts upon the lever U, through the medium of the lever86 and the roller 88, a force F, which is proportional like the force Fexerted upon the lever L, to the fuel flow rate C.

In the equilibrium condition, the lever U adopts an angular positionsuch that the following balanced equation obtains s designating thecross-sectional area of the capsules and 81 from which we obtain As thequantities a, and's are constant, the expression F is solely a functionof the distance b fl s s7 defining the position of the roller 88. Thelever U and the roller 88 thus define a force balance system with amultiplication ratio varying as a function of the angular position ofthe shaft 93. Because of the fact that the quantities F and C areproportional, we can therefore write 2 6 m constant I said quantity,which value is set by the angular position of the pilot-operated controllever 21 (possibly corrected, as before, for example as a function ofT,, in order to obtain a temperature T,, which is strictly constant). Anerror signal A C I s s7 and supplied to a motor 95, for example anelectric motor, which rotates until the position of the roller 88cancels said signal out. The equilibrium condition of the lever U isthus established and the cross-sectional area S of the nozzle,controlled by the rod 83, is then such that the quantity 0 V (and,ultimately, the

BPI4 PI7 temperature T is maintained at the set value.

Considering now, FIGS. 2 and 3, the servo control system 84 designed toregulate the cross-sectional area of the nozzle 10, will be described.This servo control is of the two-stage hydraulic type and utilizes asthe working fluid, at least in the first stage,.the pressurized fuel.

] is then generated tapped off, prior to metering, from the pipe bymeans of a high-pressure pipe 100.

The rod 83, referred to hereinbefore and cooperating with the forcebalance system U, is fixed to a first spool 101 sliding in a cylinder102 formed in a second spool 103. The spool 101, in cooperation with thecylinder 102, defines three chambers 104, 105, 106. The terminalchambers 104 and 106 are connected with one another through a passage107 and with a low pressure space BP. The central chamber 105communicates with the high-pressure line 100. The spool 103 is integralwith a shoulder 108 forming a piston sliding in a cylinder 109. Thepiston 108 delimits, in cooperation with the cylinder 109, two chambers110, 111 which communicate through respective passages 112, 113 withopenings 114, 115 formed in the wall of the cylinder'102. The rod 83which is integral with the spool 101 is maintained constantly in contactwith the lever U under the action of a spring 1 16.

There also extends from chamber 110 a line 117 terminating in ahydraulically operated valve device 118 (see FIG. 2). This valve devicecomprises, in particular, a spool 119 biased in the closing direction bya spring 120 and urged in the opening direction by the pressure of acontrol fluid. The latter can advantageously be constituted by thepressurized fuel tapped off, through a line 121, between the valvedevice 70 and the disengageable coupling 55. In the configurationillustrated in FIG. 2, the valve device 70 is closed. In thisconfiguration, the valve device 118 is subjected to the action of thespring 120 only, and is thus also closed.

The spool 103 slides in a cylinder 122, cooperating therewith to delimitthree chambers 123, 124, 125. The

two terminal chambers 123, 125 communicate through lines 126 and 127with a low-pressure space BP whilst the central chamber 124 is connectedthrough a line 128 to a high-pressure fluid source HP. Openings or ports129, 130 formed in the wall of the cylinder 122 communicaterespectively, through the medium of lines 131, 132, with two chambers ofat least one double-acting ram 133 designed to operate the flaps 11 ofthe nozzle. The reference 133a has been used to designate the movingelement or rod of the ram or jack.

In the configuration of FIG. 3, the spool 101 is in a central positionin which it closes off the ports 114, 115. The piston 108 and,consequently, the spool 103 then likewise adopt a central position inwhich the ports 129, 130 are closed off this immobilizing the rod 133aof the ram and thus that of the flaps 11, in a position which defines acertain cross-sectional area S in the nozzle.

In the event of imbalance of the force balance system U, the rod 83 actsin an appropriate direction upon the spool 101 producing a displacement,in the same direction of the spool 103 at a rate which is a function ofthe position of the spool 101 in relation to the ports 114, 115, that isto say of the amplitude of the imbalance in the system U, the centralposition of the spool 101 corresponding to the stationary condition inthe spool 103 (the system is referred to as having an integralresponse). The pressurized fluid coming from the line 128 thenpenetrates one or the other of the two working spaces of the ram 133 inorder to produce the desired variation in the cross-sectional area ofthe nozzle.

The mode of operation just described, of the servo control system 84 foroperating the nozzle flaps, is valid 7 value of the control parameteronly for the case where the valve device 118 is in the closed position.In the opposite case, the line 117 communicates through the medium of aline 134, with a low-pressure space BP so that the spool 103 comes upagainst the left-hand stop (see FIG. 3). The flaps 11 then take up theirfully open position in which the cross-sectional area of the nozzle 10is maintained at its maximum value whatever the position of the forcebalance system U.

In normal operation, the computer device E simultaneously generates afirst error signal AN and a second error signal A i The first errorsignal controls, in automatic fashion as we have seen, the

Q in order to ef- P fect control of speed, whilst the second acts uponthe cross-sectional area of the nozzle 10 in order to effect control ofthe temperature T said temperature being represented by the quantity CThe choice of this quantity, in accordance with one of the features ofthe invention, to represent the temperature T is an advantageous onesince it makes it possible simultaneously to increase the accuracy ofcontrol and also its sensitivity, in particular to the cutting-in of theafter-bumer. The control of the crosssectional areaof the nozzle duringacceleration phases, in particular in the afterbuming configuration, ismuch more rapid whilst disturbances in the speed of rotation arereduced. In a general way, acceleration times are considerablyshortened. In addition, the effect upon the control system of possiblevariations in the Reynolds number of the flow or of tapping off of airor power (for example in the case of a dual-flow turbojet engine,through the by-pass 19 shown in FIG. 1), is drastically reduced.

In the event of failure of the computer device E or any of the elementsof the system which controls the temperature by acting upon thecross-sectional area of the nozzle, there is provided in accordance withanother aspect of the invention an emergency control system based upondirect manual control of the ratio To this end, the pilot effects theopening of the valve device by switching in the electrical circuit 700.The pressurized fuel coming from the line 69 then, on the one handcontrols the engagement of the coupling 55 and, on the other, throughthe medium of line 121, ef fects the opening of the valve device 118.

Because of the engagement of the coupling 55, the movements of thepilot-operated lever 21 are transmitted directly to the shaft 48. Thepilot is thus able to vary, within certain limits fixed by the range ofdeployment of the lever 21 and without exceeding the stabilizedoperating range of the power plant, to vary the value of the ratio C Toeach of the values of this ratio (and it will be noted that said ratiocan be generated with very high accuracy), there corresponds a workingpoint with a temperature T which is maintained at an approximatelyconstant safe value. Selfevidently, the torque-limiter 53 is set so thatthe intervention of the pilot overrides the automatic control 50,

51, 52, 53. In addition, the opening of the valve device 118 results inthe nozzle flaps 11 moving into their maximum aperture position andbeing maintained there. This arrangement constitutes a safety measurewhich, when the emergency control system is operating, avoidsinopportune variations in the temperature T consequent upon uncontrolledvariations in the cross-sectional area of the nozzle.

Thus, by utilizing certain elements of an existing automatic controlsystem and without further complicating the power plant other than bythe addition of simple elements (disengageable coupling 55, valvedevices 70 and 118, torque-limiter 53), a particularly reliable andeffective emergency control (direct control) is created. This emergencycontrol could also, if required, be supplemented by an automatictemperature control system of another kind than the one specificallydescribed hereinbefore.

It goes without saying that the embodiments described are merelyexamples and are open to modification, in particular by the substitutionof equivalent techniques, without in so doing departing from the scopeof the invention.

We claim:

1. In and for a gas turbine power plant which comprises a compressor, acombustion chamber supplied with air coming from the compressor and withfuel, a turbine supplied with combustion gases coming from thecombustion chamber, and a nozzle for discharging the combustion gasescoming from the turbine, an improved device comprising:

means for regulating the fuel flow to the combustion chamber;

means for varying the cross-sectional area of the nozzle; and means forcontrolling the nozzle cross-sectional area varying means as a functionof the fuel flow rate C delivered to the combustion chamber, the staticair pressure P, at exit from the compressor, and the static gas pressureP., at the turbine exit, so that at least under certain conditions ofoperation, an output quantity defined by the expression 0' 6P I4 P I1 inwhich )8 designates a constant coefficient of reduction, has a desiredpredetermined value. 2. A control device as claimed in claim 1,comprising means for producing as a function of the fuel flow rate Cdelivered to the combustion chamber, of the static pressure P. of theair at the exit from the compressor and of the static pressure P,, ofthe gases at the exit from the turbine, a first signal which is afunction of the output quantity 0' means for producing BPI4 PI7 a secondsignal or reference signal .mp T

which is a function of said desired predetermined value means forproducing a third signal or error signal which is a function of thedifference [BPB| PI7] balance system with a variable multiplicationratio, which is subjected to a first force as a function of the fuelflow rate C and to a second force as a function of the pressuredifference BP., and means for generating a signal which is a function ofsaid multiplication ratio.

4. A control device as claimed in claim 2, also including apilot-operable control lever, and wherein the reference signalgenerating means comprises means sensitive to the position of saidlever.

5. A control device as claimed in claim 4, wherein said reference signalgenerating means also includes means sensitive to at least one otherparameter of the power plant, in particular the total temperature of theair at the compressor intake.

6. A control device as claimed in claim 3, wherein the means sensitiveto the error signal and designed to control the variation in thecross-sectional area of the nozzle, comprises means which are sensitiveto the instantaneous position of said force balance system and means formodifying, as a function of said error signal, the multiplication ratioof said force balance system.

7. A control device for a gas turbine power plant of the type comprisinga compressor, a combustion chamber supplied with air coming from thecompressor and with fuel, a turbine supplied with combustion gasescoming from the combustion chamber, and a nozzle for discharging thecombustion gases coming from the turbine, said device comprising:

means for regulating the fuel flow to the combustion chamber;

means for varying the cross-sectional area of the nozzle; means forcontrolling the nozzle cross-sectional area varying means as a functionof the fuel flow rate C delivered to the combustion chamber, the staticair pressure P. at exit from the compressor, and the static gas pressureP, at the turbine exit, so that at least under certain conditions ofoperation, an output quantity defined by the expression C BPI4-PI7 inwhich B designates a constant coefficient of reduction, has a desiredpredetermined value; and manual control system operable in an emergencyfor controlling the fuel flow regulating means.

8. A control device for a gas turbine power plant of the type comprisinga compressor, a combustion chamber supplied with air coming from saidcompressor and with fuel, a turbine supplied with combustion gasescoming from the combustion chamber, and a nozzle for discharging thecombustion gases coming from said turbine, said control devicecomprising, in com bination:

means for regulating the rate of fuel flow to the combustion chamber;means operable to vary the crosssectional area of the nozzle betweenmaximum and minimum limits; an automatic control system for operatingsaid nozzle cross-sectional area varying means;

a normally inoperative manual control system for controlling the fuelflow regulating means;

combustion gases at the turbine intake at a predetermined safe value.

9. A control device according to claim 8, wherein the means foractivating the manual control system comprise a normally disengagedcoupling between said manual control system and said means forregulating said fuel flow, and control means for engaging said coupling.

10. A control system according to claim 9, wherein said coupling isoperated by fluid pressure, and said control means comprise a valvearranged between a source of pressurized fluid and said coupling andadapted in its open position to supply said coupling with said fluid.

1 l. A control system according to claim 10', wherein said meansoperative to open the nozzle to maximum limit comprise pressuresensitive means responsive to the pressure of said pressurized fluiddownstream of said valve.

12. A control system according to claim 8, wherein the means forregulating the fuel flow rate to the combustion chamber is controlled asa function of the fuel flow-rate C delivered to said combustion chamberand of the static air pressure P. at the compressor exit, so that anoutput quantity defined by the ratio C is P, maintained at apredetermined value; and wherein activation' of said manual emergencycontrol system modifies said value.

1. In and for a gas turbine power plant which comprises a compressor, acombustion chamber supplied with air coming from the compressor and withfuel, a turbine supplied with combustion gases coming from thecombustion chamber, and a nozzle for discharging the combustion gasescoming from the turbine, an improved device comprising: means forregulating the fuel flow to the combustion chamber; means for varyingthe cross-sectional area of the nozzle; and means for controlling thenozzle cross-sectional area varying means as a function of the fuel flowrate C delivered to the combustion chamber, the static air pressure Psat exit from the compressor, and the static gas pressure Ps at theturbine exit, so that at least under certain conditions of operation, anoutput quantity defined by the expression C/( Beta Ps - Ps ), in whichBeta designates a constant coefficient of reduction, has a desiredpredetermined value.
 1. In and for a gas turbine power plant whichcomprises a compressor, a combustion chamber supplied with air comingfrom the compressor and with fuel, a turbine supplied with combustiongases coming from the combustion chamber, and a nozzle for dischargingthe combustion gases coming from the turbine, an improved devicecomprising: means for regulating the fuel flow to the combustionchamber; means for varying the cross-sectional area of the nozzle; andmeans for controlling the nozzle cross-sectional area varying means as afunction of the fuel flow rate C delivered to the combustion chamber,the static air pressure Ps at exit from the compressor, and the staticgas pressure Ps at the turbine exit, so that at least under certainconditions of operation, an output quantity defined by the expressionC/( Beta Ps - Ps ), in which Beta designates a constant coefficient ofreduction, has a desired predetermined value.
 2. A control device asclaimed in claim 1, comprising means for producing as a function of thefuel flow rate C delivered to the combustion chamber, of the staticpressure Ps of the air at the exit from the compressor and of the staticpressure Ps of the gases at the exit from the turbine, a first signalwhich is a function of the output quantity (C/( Beta Ps - Ps )) ; meansfor producing a second signal or reference signal (C/( Beta Ps - Ps ))which is a function of said desired predetermined value ; means forproducing a third signal or error signal which is a function of thedifference (C/( Beta Ps - Ps )) - (C/( Beta Ps - Ps )) ; and meanssensitive to said error signal in order to control the variation in thecross-sectional area of the nozzle.
 3. A control device as claimed inclaim 2, wherein the means for generating the signal which is a functionof the quantity (C/( Beta Ps - Ps )) comprises a force balance systemwith a variable multiplication ratio, which is subjected to a firstforce as a function of the fuel flow rate C and to a second force as afunction of the pressure difference ( Beta Ps - Ps ) ; and means forgenerating a signal which is a function of said multiplication ratio. 4.A control device as claimed in claim 2, also including a pilot-operablecontrol lever, and wherein the reference signal generating meanscomprises means sensitive to the position of said lever.
 5. A controldevice as claimed in claim 4, wherein said reference signal generatingmeans also includes means sensitive to at least one other parameter ofthe power plant, in particular the total temperature of the air at thecompressor intake.
 6. A control device as claimed in claim 3, whereinthe means sensitive to the error signal and designed to control thevariation in the cross-sectional area of the nozzle, comprises meanswhich are sensitive to the instantaneous position of said force balancesystem and means for modifying, as a function of said error signal, themultiplication ratio of said force balance system.
 7. A control devicefor a gas turbine power plant of the type comprising a compressor, acombustion chamber supplied with air coming from the compressor and withfuel, a turbine supplied with combustion gases coming from thecombustion chamber, and a nozzle for discharging the combustion gasescoming from the turbine, said device cOmprising: means for regulatingthe fuel flow to the combustion chamber; means for varying thecross-sectional area of the nozzle; means for controlling the nozzlecross-sectional area varying means as a function of the fuel flow rate Cdelivered to the combustion chamber, the static air pressure Ps at exitfrom the compressor, and the static gas pressure Ps at the turbine exit,so that at least under certain conditions of operation, an outputquantity defined by the expression C/( Beta Ps - Ps ), in which Betadesignates a constant coefficient of reduction, has a desiredpredetermined value; and a manual control system operable in anemergency for controlling the fuel flow regulating means.
 8. A controldevice for a gas turbine power plant of the type comprising acompressor, a combustion chamber supplied with air coming from saidcompressor and with fuel, a turbine supplied with combustion gasescoming from the combustion chamber, and a nozzle for discharging thecombustion gases coming from said turbine, said control devicecomprising, in combination: means for regulating the rate of fuel flowto the combustion chamber; means operable to vary the cross-sectionalarea of the nozzle between maximum and minimum limits; an automaticcontrol system for operating said nozzle cross-sectional area varyingmeans; a normally inoperative manual control system for controlling thefuel flow regulating means; means for activating said manual controlsystem in the event of failure of the automatic system; and meansoperative in response to activation of said manual control system tooperate said nozzle area control means to open the nozzle to its maximumlimit, in order to maintain the temperature of the combustion gases atthe turbine intake at a predetermined safe value.
 9. A control deviceaccording to claim 8, wherein the means for activating the manualcontrol system comprise a normally disengaged coupling between saidmanual control system and said means for regulating said fuel flow, andcontrol means for engaging said coupling.
 10. A control system accordingto claim 9, wherein said coupling is operated by fluid pressure, andsaid control means comprise a valve arranged between a source ofpressurized fluid and said coupling and adapted in its open position tosupply said coupling with said fluid.
 11. A control system according toclaim 10, wherein said means operative to open the nozzle to maximumlimit comprise pressure sensitive means responsive to the pressure ofsaid pressurized fluid downstream of said valve.